Apparatus for the electro-mechanical polishing of surfaces



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Dec. 20, 1960 L. G. DAMGAARD 2,965,556

APPARATUS FOR THE ELECTRO-MECHANICAL POLISHING 0F SURFACES Filed April15, 1959 6 1234 an 9 /0 20, I f

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ATTORNEYS United States Patent APPARATUS FOR THE ELECTRO-MECHANICALPOLISHING 0F SURFACES Lam-its Gudmund Damgaard, Virum, Denmark, assignorto H. Struers Chemiske Laboratorinm, Copenhagen, Denmark Filed Apr. 15,1959, Ser. No. 806,561

14 Claims. (Cl. 204-213) This invention relates to an apparatus for theelectromechanical polishing of surfaces, especially for metallographicpurposes.

The principle of electro-mechanical polishing consists in subjecting asample or workpiece to electrolytical polishing and at the same time toa sweeping action which may solely serve to secure a better uniformityof the electrolytical polishing effect or alternatively may add apolishing eifect of a more or less abrasive nature. In the former case,the sweeping will be made by means of a cloth without the use of anyabrasive material in the cloth or in the electrolyte and the effect ofthe sweeping will be to remove any films or deposits that may tend tobuild up as a consequence of the electrolytical polishing. In the lattercase, an abrasive effect may be obtained by using a waterproof abrasivesheet or a cloth having abrasive particles distributed therein or againabrasive particles may be suspended in the electrolytic liquid used forthe electrolytical polishing.

For the electro-mechanical polishing, apparatuses have been proposed,which comprise a revolving disc on which a polishing cloth or polishingsheet is stretched o-r clamped by means of a clamping ring, which at thesame time forms a peripheral wall surrounding the disc and extendingupwards therefrom so that the disc and ring combine to form a shallowcup in which a certain amount of electrolyte can be received. Theseknown apparatuses suffer from the drawback that it is very diificult toavoid leakage of electrolyte between the engaging surfaces of the discand the ring and beside the operation is relatively slow, because thespeed of rotation must be kept low in order to keep a layer ofelectrolyte over the whole surface of the disc.

It is an object of the invention to construct an apparatus, which iscapable of holding a quantity of electrolyte during operation in such amanner that no leakage of liquid will take place.

Another object of the invention is to construct an electro-mechanicalpolishing apparatus which is capable of satisfactory operation at arelatively high speed of rotation.

A further object of the invention is to devise an electro-mechanicalpolishing apparatus of a simple and reliable construction and whichcombines the advantages of non-leaking properties with the advantage ofa simple and satisfactory attachment of a polishing cloth to the surfaceof a rotatable disc.

With these and other objects in view, which will be apparent to a manskilled in the art from the following description, the invention residesin the novel elements, combinations and structural arrangements setforth in the appended claims.

The invention will now be described in further detail with reference tothe accompanying drawings, in which Fig. 1 shows a vertical sectionthrough one form of an electro-mechanical polishing apparatus accordingto the invention,

Fig. 2a plan view of same, and

Fig. 3 on a larger scale a section through the polishing disc of theapparatus of Figures 1 and 2.

In the drawing, 1 represents a horizontal table carried by a frame,which is not shown in the drawing. The table 1 has a circular hole 2, inwhich an open-topped vessel 3 is arranged to revolve. The vessel 3 iscarried by a vertical shaft 4, which is rotatably mounted in the frameof the apparatus and coupled to suitable driving means not shown in thedrawing such as an electric motor and suitable gear mechanism. Thevessel 3 has a bottom 5 and an upstanding peripheral wall 6, which isintegral with the bottom 5. The peripheral wall 6 has an outer diameterwhich is smaller than the inner diameter of the hole 2 so that anannular gap is formed between the peripheral wall and the edge of thehole. The bottom 5 of the vessel is constructed with a central raisedportion 7, at the middle of which a screw threaded metallic hub member 8is embedded in such a manner as to have its upper surface flush withthat of the raised portion 7, A polishing disc 9 is constructed on itsunderface with a hub portion 10 and a screw threaded pin 11 dependingtherefrom. By screwing the pin 11 into the screw threaded hole of thehub member 8, the polishing disc can be rigidly mounted in the vessel ina position slightly above the bottom of the latter.

12 is a polishing cloth which is stretched on the surface of thepolishing disc 10 so as to form a smooth and crease-free polishingsurface. The nature of this polishing cloth will be selected accordingto the nature of the work to be carried out. It has been found in manycases where the effect of the mechanical polishing is mainly that ofremoving films and deposits from a workpiece being polished, that apolishing cloth according to the following specification will besatisfactory:

Zein cloth, plain weave,

Warp: 2/60 metric count with 780 spinning twist and 760 twisting twiststaplelength 4 inches, 63 picks per inch,

Weft: As warp.

of the polishing disc as a sort of elastic cover which will then bestretched taut on the upper surface of the polishing disc by means ofthe contracting force of the annular elastic member, or alternatively asimple, substantially non-elastic cord may be used which will then betautened manually. At its centre, the polishing cloth has a hole 15, theedge of which is reinforced by means of a washer 16 of a thermoplasticmaterial located on the inner side of the polishing cloth and unitedtherewith. by heat and pressure. The function of the hole 15 is topermit the escape of gases that will be developed at the surface of thepolishing disc owing to the electrolytical action and, if not permittedto escape, might cause the polishing cloth to bulge.

Mounted in the hole 2 of the table 1 in a position around and below therotatable vessel 3 is a stationary shield 17 which is constructed toform an annular trough 18 to receive any electrolyte that may splashover the edge of the vessel 3 in operation. The shield 17 rests on theedge of the hole 2 by means of a flanged portion 19.

A stationary cylindrical ring 20 is mounted around the revolving vessel3 in such a manner as to extend downwards into the gap between theshield 17 and the vessel 3 and to extend upwards to a level above theupper edge 0f the peripheral wall 6 of the vessel 3. The ring 20 is.

provided with lugs 21 having threaded holes receiving screws 22 by meansof which the ring is supported on the flange 19 of the shield 17 andthereby indirectly on the table The ring 20 carries a bracket 23, whichextends inwards from the ring and serves to support a scoop member 24,which extends downwards into the inner space of the vessel 3. The scoopmember has a bottom wall 25 in a position adjacent the surface of thepolishing cloth 12 and also a vertical upstanding wall 26, by means ofwhich the scoop member is carried from the bracket 23. The upstandingwall 26 of the scoop member is curved in such a manner that the outerend portion of the same is directed substantially tangentially of thecircular move,- ment of the vessel while the inner end portion of theupstanding wall 26 is directed substantially towards the axis ofrotation of the vessel. The bottom wall 25 is fiat and is constructedwith a substantially V-shaped notch 27 in its front edge.

It'will be understood that when the vessel 3 revolves inthe direction ofthe arrow shown in Figure 2, the liquid will .be urged outwards and willtend to form aliquid ring adjacent the peripheral wall 6 as indicated inFigure 1. In fact, if no special measures were taken, the centralportion of the polishing cloth would be dried out already at a verymoderate speed of rotation. However, in the construction shown, liquidwill constantly be scooped from the liquid ring by the scoop member 24and thereby will be redirected towards the centre of the vessel so thatthere will be a constant flow of liquid from the centre towards theperiphery. In this manner it is possible to keep a suflicient film ofliquid on top of the polishing cloth even at relatively high speeds ofrotation.

By adjusting the screws 22, the scoop member may be correctly positionedrelative to the revolving vessel. In addition to this adjustingfunction, the ring 20 has the additional purpose of collecting anysplashes from the revolving vessel so that the liquid thus collected mayflow down into the annular trough 18. In this manner the surroundingsare protected from splashes of electrolyte.

Current is supplied to the disc 9, which is effective as cathode in theelectrolytic process, by means of a stationary contact 28 mounted in thebracket 23 and engaging a contact ring 29 mounted below the bottom ofthe vessel 3 and extending radially therefrom so as to form a freecontact surface for engagement by the stationary contact 28. The contactring 29 is connected to the metallic hub member 8 by means of anelectric conductor 30. The anode in the electrolytical polishing processis formed by the workpiece itself, to which current is supplied inaccordance with well known principles. Figure 1 shows a metallographicsample 31 which is embedded in a thermoplastic material 34 and to whichcurrent is supplied from the positive pole of a source through a metalrod 35 which at the same time serves to press the sample against thesurface of the polishing cloth. The sample may be held by hand or by asample holder in the same manner as in conventional mechanicalpolishing.

The direct current supply described may if desired be replaced byalternating current supply, such as is desirable for certainmetallographic purposes.

If a sample slips during the performance of the electromechanicalpolishing, it is important that this should not be thrown out into theliquid ring because it might then give rise to splashing. In theillustrated apparatus, such a sample will in many cases jump into thelap of the scoop member to be caught thereby, but in some cases it mightbe arrested by the front edge of the bottom wall of this member andmight then slide along this front edge into the liquid ring. Theprovision of the notch 27 in the said front edge serves to stop suchoutward travel of samples that are arrested already when striking thefront edge.

I claim:

1. An apparatus for the electro-mechanical polishing of -surfacescomprising a flat open-topped vessel mounted for rotation about asubstantially vertical axis, said vessel having a bottom and anupstanding peripheral wall integral therewith, a fiat disc forming aseparate part mounted on the bottom of said vessel for rotationtherewith, said disc being coaxially disposed with respect to saidvessel and being located in its entirety below the upper edge of saidside wall, a polishing cloth stretched on the top surface of said discindependently of said vesseLand means for supplying current to saiddisc.

2. An apparatus as in claim 1, in which said polishing cloth is in theform of a circular piece of cloth having a doubled over marginal portionprovided with contraction means.

3. An apparatus as in claim 2, in which said contraction means is in theform of an annular elastic member in a casing formed along the edge ofthe polishing cloth.

4. An apparatus as in claim 1, in which cooperating screw means areprovided in a central position on the underface of the polishing discand the bottom of the vessel respectively.

5. An apparatus as in claim 4, and further comprising a contact ringmounted on said vessel and engaged by a stationary current supplycontact, and an electric connection between said contact ring and saidscrew means at the bottom of said vessel.

6. An apparatus as in claim 1, in which scoop means is provided forscooping liquid adjacent the peripheral wall of said vessel anddirecting same towards the centre of the vessel.

7. An apparatus as in claim 6, in which said scoop means has a flatbottom wall and a curved upstanding wall directed substantiallytangentially of the circular movement of the vessel at one end thereofand directed substantially towards the axis of rotation of the vessel atthe other end thereof.

8. An apparatus as in claim 7, in which the bottom wall of said scoop isconstructed with a substantially V- shaped notch in the front edgethereof.

9. An apparatus as in claim 1, in which said polishing cloth is in theform of a circular piece of cloth having a central hole.

10. An apparatus as in claim 9, in which the portion 'of said clothimmediately surrounding said hole is reinforced by means of a flatannular washer united with the fabric of the cloth.

11. An appara us as in claim 10, in which said washer consists of athermoplastic material.

12. An apparatus for the electro-mechanical polishing of surfaces,comprising a table having a circular hole, a flat open-topped vesselmounted for rotation about a substantially vertical axis coinciding withthe axis of said hole, said vessel having a bottom and an upstandingperipheral wall integral therewith, the outer diameter of saidperipheral wall being smaller than the diameter of said hole, a fiatdisc forming a separate part mounted on the bottom of said vessel forrotation therewith, said disc being coaxially disposed with respect tosaid vessel and being located in its entirety below the upper edge ofsaid side wall, a polishing cloth attached to said disc independently ofsaid vessel, means for supplying current to said disc, a stationarycylindrical supporting ring having a diameter smaller than that of thehole in said table, but larger than the outer diameter of said vessel,said supporting ring being constructed intermediate of its height withlugs having screw-threaded holes to receive screws for supporting saidsupporting ring in points adjacent the edge of the hole of said table,the supporting ring having such dimensions as to extend downwards belowthe level of the table and upwards above the level of the upper edge ofthe peripheral wall of said vessel, a bracket carried by said supportingring and extending inwards there from above the level of the upper edgeof said vessel, a scoop member carried by said bracket and extendingdownwards therefrom into the interior of said vessel, said scoop memberbeing arranged to scoop liquid adjacent 5 8 the peripheral wall of saidvessel and to direct same tosaid vessel is constructed with a raisedportion at me wards the center of the vessel. middle thereof. 13. Anapparatus as in clai m 12 and further comprising I a contact ringmounted on the underface of said vessel in References Cited in the filof this pate! a position so as to extend radially therefrom, astationary 5 current supply contact mounted in said bracket and engag-UNITED STATES PATENTS ing the upper surface of the radially extendingportion of 646,313 Rhodin Mar. 27, 1900 said contact ring, and anelectric connection between said 2,206,908 Lunt July 9, 1940 contactring and said disc. 2,539,455 Mazia J an. 30, 1951 14. An apparatus asin claim 1 in which the bottom of 10 2,741,594 Bowersett Apr. 10, 1956

1. AN APPARATUS FOR THE ELECTRO-MECHANICAL POLISHING OF SURFACESCOMPRISING A FLAT OPEN-TOPPED VESSEL MOUNTED FOR ROTATION ABOUT ASUBSTANTIALLY VERTICAL AXIS, SAID VESSEL HAVING A BOTTOM AND ANUPSTANDING PERIPHERAL WALL INTEGRAL THEREWITH, A FLAT DISC FORMING ASEPARATE PART MOUNTED ON THE BOTTOM OF SAID VESSEL FOR ROTATIONTHEREWITH, SAID DISC BEING COAXIALLY DISPOSED WITH RESPECT TO SAIDVESSEL AND BEING LOCATED IN ITS ENTIRETY BELOW THE UPPER EDGE OF SAIDSIDE WALL, A POLISHING CLOTH STRETCHED ON THE TOP SURFACE OF SAID DISCINDEPENDENTLY OF SAID VESSEL, AND MEANS FOR SUPPLYING CURRENT TO SAIDDISC.